Chronic heart failure (CHR) appears to affect a relatively large and potentially increasing segment of the population. See, e.g., The Task Force on Heart Failure of the European Society of Cardiology. Guidelines for the Diagnosis of Heart Failure, 16 Eur. Heart Jnl., p. 741-751 (1995). In addition, many elderly heart failure patients are women, and the more common cause of the syndrome may be diastolic dysfunction. Early diagnosis of heart failure, particularly heart failure due to diastolic dysfunction, in which ejection fraction may be normal, remains a challenge. Documentation of pulmonary congestion in the absence of evidence for systolic dysfunction is believed to represent reasonable criteria for this diagnosis. See Tan et al., Heart Failure in Elderly Patients: Focus on diastolic Dysfunction, Heart Failure: Scientific Principles and Clinical Practice, P.A. (Churchill-Livingston, NY, Poole-Wilson, Ed. 1997).
For other cardiopulmonary or respiratory disorders or diseases, patients may exhibit a shortness of breath of uncertain etiology that can make it difficult to identify the disorder or condition and/or to thus treat in an effective manner. For example, in response to administration of pharmacological agents, some patients may experience respiratory distress. Early identification of drug-induced pulmonary reactions or disorders may inhibit lung injury.
Gas transfer from ambient air to the blood involves different in vivo transport mechanisms. Generally described, alveolar ventilation is accomplished by convective and diffusive transport. Gas transfer within the alveolus and from the alveolus into the blood stream occurs by diffusion along concentration gradients. The blood is then transported from the lungs to peripheral tissues by convective transport. These transport processes can be affected by a number of lung diseases. Convective transport in the airways is thus impaired in obstructive lung diseases. See Alderson PO, Line BR. Scintigraphic evaluation of regional pulmonary ventilation. Semin Nucl Med 1980; 10:218-242. Diffusion impairment can occur in interstitial lung diseases as well as in pulmonary edema. See Puri et al., Reduced alveolar-capillary membrane diffusing capacity in chronic heart failure. Its pathophysiological relevance and relationship to exercise performance, Circulation 1995; 91:2769-2774, V-16. The pulmonary vasculature can be affected by both primary lung disease and by left heart failure, causing abnormalities in blood flow. Worsley et al., Ventilation-perfusion lung scanning in the evaluation of pulmonary hypertension. J Nucl Med 1994; 35:793-796.
In view of the above, there remains a need for a minimally invasive in vivo method of evaluating a patient to identify the underlying condition(s) so that appropriate treatments can be pursued, certain medicaments initiated or ceased, and/or to evaluate the efficacy of therapeutic treatments administered to treat those conditions.